Many disc-like objects such as CDs (compact discs), DVDs (digital versatile discs or digital video discs), HD-DVDs (high definition DVDs), BDs (Blu-ray discs), etc., have center holes and are mass produced along a production line that involves processes which require retrieval of the topmost such object from a vertical stack of similar objects. Such production processes include, for example, printing or otherwise applying text and/or graphics on unfinished discs, inserting a finished disc in a carrier case or other packaging, etc.
As the discs are transported from one process to another, they are typically transported in a vertical stack, such as on a spindle that penetrates the center holes of the discs.
The topmost disc is removed from the stack by a handling device or mechanism that can include a robotic arm and a device referred to in the art as a “picker”. The robotic arm positions the picker which engages the disc. The robotic arm then moves the engaged disc from the stack to a desired location on the production line where the picker then releases the disc. Some conventional pickers generally employ vacuum or suction from above the topmost disc to retrieve that disc from the spindle stack. Other conventional pickers mechanically grasp the topmost disc along the outer edge of the object and/or the inner edge bordering the center hole of the disc.
In many conventional production systems, the handling device is accompanied by a movable disc carrier platform (not shown) including a center hole through which the spindle fits. After a disc is removed from the spindle, the stack of discs is elevated a distance equal to the thickness of the disc, so that the topmost disc in the stack is at a predetermined position relative to the stack.
A problem that exists with many conventional handling devices, such as mentioned above, is the unintended retrieval of multiple discs from the stack in a particular handling cycle. This problem leads to downtime in the manufacturing process and often requires operator intervention, thus increasing production cost.
The causes of this problem include buildup of static charge on the discs, moisture between contacting surfaces of adjacent discs, and/or the formation of a vacuum between adjacent discs.
A variety of approaches for separating the topmost disc from other discs in a stack have been proposed. For example, a compact disc gripper device has been proposed for gripping a topmost CD off a vertical stack of CDs. Other approaches have proposed adding spacers between adjacent discs in a stack. Another approach proposes blowing ionized air from the outer side face of the stack.
The above mentioned prior arts suffer from several disadvantages. For example, the gripping mechanisms described above require the replacement of current disc handling mechanisms at multiple sites along each production line, thereby injecting additional complexity and cost to the manufacturing process. The spacers described above minimize the number of discs that can be accommodated on a stack of a predetermined height and also require additional means for inserting and removing the spacers. The application of ionized air to the outer side face of the stack has been shown not to work effectively.
Consequently, there exists a need for improved techniques for separating a topmost disc from a stack of discs.